Caribou (Rangifer tarandus) are an integral part of the ecological and cultural fabric of northwest Alaska. Western Arctic Herd (WAH) caribou roam over this entire region, including all 5 Arctic Network Inventory and Monitoring Program (ARCN) National Park Units. Conservation of healthy caribou populations are specifically mentioned within the enabling legislation (Alaska National Interested Lands Conservation Act or ANILCA) of three of these Parks and is of critical concern to subsistence hunters within this region. Caribou are, by far, the most abundant large mammal in northwest Alaska and are famous for their long-distance migrations and large population oscillations. For these reasons, ARCN chose WAH caribou as a Vital Sign for long term monitoring. This report documents the monitoring results of this Vital Sign during its 3rd year (September 2011 - August 2012) of implementation. Results from the first 2 years of monitoring are also included for ease of comparison.